package problem115;

//115.不同的子序列
//https://leetcode.cn/problems/distinct-subsequences/

class Solution {
    public int numDistinct(String s, String t) {
        int n = s.length(), m = t.length();
        int[][] dp = new int[m+1][n+1];
        for(int i = 0; i<=n; i++) {
            dp[0][i] = 1;
        }
        for(int i = 1; i<=m; i++) {
            for(int j = 1; j<=n; j++) {
                dp[i][j] = dp[i][j-1];
                if(t.charAt(i-1) == s.charAt(j-1)) {
                    dp[i][j] += dp[i-1][j-1];
                }
            }
        }
        return dp[m][n];
    }
}

/*
dp[i][j]: s串的0~i之间的子序列中 t子串(0~j)的出现次数
*/